Attention-Deficit/Hyperactivity Disorder (AD/HD) is the diagnosis used to describe children who are inattentive, impulsive, and hyperactive. The cause is unknown and is thought to be biological and multifactorial. Previous work has shown that a subpopulation of children with ADHD (L- AD/HD) have low blood levels of key derivatives of essential fatty acids (EFA) and a greater frequency of physical symptoms indicative of EFA deficiency. Essential fatty acids are of two types, n-3 and n-6, and derivatives of both types were depleted in the plasma of L-ADHD. The long-term goals of this research program are to determine the relationship between low EFA status and behavioral problems in children with L-AD/HD, and to elucidate the cause for the low EFA status. To begin to achieve these goals a pilot study involving children with L-AD/HD will be conducted to test a two-part hypothesis: (1) that oral supplementation of specific fatty acids will increase the concentrations of long chain n-6 and n-3 fatty acids in the blood, and (2) that increased blood fatty acid levels will result in improved behavior. For this pilot study subjects with AD/HD (n=90) who have many symptoms of EFA deficiency and lower levels of blood EFA will be recruited. A supplement containing the specific EFA derivatives that are depleted in these children will be used in a double-blind intervention study with a 3-group parallel (noncrossover) design. The subjects will be selected based on the results of prescreening blood tests and symptom analysis. The L-AD/HD subjects will be randomly assigned to 3 groups: Group A will receive a high dose active supplement, Group B will receive low dose active supplement and Group G will receive placebo capsules. The three groups will be balanced with respect to initial behavioral assessment, math achievement, age, gender, socioeconomic and medication status. Blood samples will be drawn at baseline, 2 and 4 months of supplementation for analysis of fasting plasma and red blood cell fatty acids. Behavioral and learning assessments will be conducted before supplementation begins, during, and at the end of the 4 month intervention.